Process of drying varnish films



Patented Dec. 30, 1930 UNITED STATES PAUL B. COCHBAN, F WILKINSBURG, PENNSYLVANIA, ASSIGNOR '10 WESTINGHOUSE PATENT OFFICE ELECTRIC & MANUFACTURINGCOMPANY, A CORP O RATION OF PENNSYLVANIA rnocnss or DRYING vARNIsn nuts No Drawing.

i0 and other accessories entering into the manu-- facture of electrical machinery.

Another object of my invention is to provide a method of decreasing the time necessary for drying the insulating-varnish films that are applied to fibrous-insulated coils embedded in the slots of alternating-current generators which consists essentially in wrapping the coils with a fibrous material, such as silk or cotton tape, and impregnating the fibrous material with ozonized air, so that,

when an insulating-varnish film is subsequently applied, its rate of drying will be accelerated, and a completely dried film will be produced in a comparatively short period of .25 time.

In the usual process of drying insulating varnishes applied to fibrous-insulated coils,

such as are provided in alternating-current generators, it has'been'the practice to wrap the conductors orcoils with fibrous insulation, such as cotton or silk tape, and to 'heat the fibrous insulated coil in 'air,.ieither.before or after it has beenplaced; in the slotsof electrical apparatus, at "a temperature of about 105 to 110 0., and, after cooling to about 70 (3., the coil, or the rotor or stator, with thecoils embedded inthe slots, is dipped into an insulating varnish which is subsequently 40 baked to dry the varnish film.

suming process.

The drying of such varnish films, which are usually composed of a resin, a vegetable dry ing oil and a volatile thinner, is a timecon- Space and equipment are: utilized for long periods. of time, making Application filed January 16, 1928. Serial No. 247,265.

the varnish, or the addition of metallic driers,

such as metallic soaps of oil or resin acids.

Elevated temperatures hasten the evaporation of the thinner and accelerate the oxidation of the oil, but such temperatures have a tendency to cause deterioration of the oil and resin, so that a film produced in this manner is; often of an inferior quality, and care must be exercised to keep the temperature. below the boiling point of the thinner, as the use of such a baking heat causes a rapid evolution of the vapors of the thinner, resulting in a crazed and blistered film.

When the fibrous-insulated conductors or coils are embedded in the slots of the stator or rotor of an alternating-current generator and the assembled parts are subsequently immersed in an insulating varnish, the drying of the varnish film on the impregnated fibrous insulation is unusually slow, because the varnish is deep in the slots where it is not readily accessible to the oxidizing action of the air and it has, therefore, been found very difficult to secure a completely dried varnish film in a resonable length of time.

I have made the discovery that, if the stator or rotor withthe fibrous insulated coils embedded in their-,respective, slots, is first preheated in an atmosphere of ozonized airs-instead of dry air until the coils have attained a temperature of about 105 C. and then slowlycooled to about in air or, preferably, in an atmosphere-of ozonized air, and the stator or rotor, or the fibrous insulated cpils alone, are then impregnated with an inwill be materially expedited.

The following experiments. will serve to illustrate and explain theessential-featurtas:

of my invention. -A test block having a slot, lined with cloth similar to those on the rotor of an alternating-current generator were pro-, vided. Testbars of cold-rolled steel, each spirally wound with two layers of cotton tape .75 inches wide and .007 inches thick and each layer being overlapped one-half of. its distance, were placed above; each other in the slot. The insulated conductor was then inserted in the slot, and a fibre wedge was placed over the top bar.

si'ilating-varnish, the drying of the varnish 40 hours .l r.

Six blocks, prepared in this manner, were placed in an electrically heated oven, and ozonized air, having a concentration of 25% ozone, was passed through the oven at the rate of 7 liters per minute until they had attained a temperature of 150 C, The blocks containing the insulated coils were then cooled slowly to C. inthe same atmosphere. They were then dipped in an. insulating-oil varnish composed of an asphaltic gum, a vegetable drying oil and a volatile thinner, for thirty minutes. After. draining for ten minutes, the blocks were placed in an electrically heated oven maintained at a temperature of 105 to 110 C. and the resistance of each coil was measured at various intervals.

Six additional slotted blocks,-having coils embedded in the slots, were impregnated with the same varnish after being prepared in a similarmanner, with the exception that they Average hot resistance in megohms--temperature 105-110 Ifrehcated 1n ozone Preheated Time in dry air 10 hours 20 hours 3O hnnrs Itis well-known that the resistance of such insulating material varies inversely with its temperature. However, as the oxidation and the drying of the varnish proceeds, the resistance gradually increases and the resistance is, therefore, a true indication of the drying of the varnish. The remarkable increase in the resistance of the insulating material which had been pre-heated in ozonized air shows that the oxidation and dr ing of the varnish proceeds much more rapi ly than when it is re-heated in air.

While do not wish to be limited'to any particular theory that now prevails or may be later develo ed, I am of the opinion that the increase 0 resistance is caused b the fibrous insulation retaining a considerable quantity of the ozonized air in the fibers: The ozone may beicombined, either physically or chemically, with the fibers, or there may be a artial; chemical and a partial physical reaction, but the experiments that I have made clearly demonstrate that the ozone .or

ozonated' fibers-aid materially in the oxidation and drying of the varnish.

The following additional tests of the dryin time of varnishes applied to fibrous insu ated coils which have been preheated in dry air, as compared with those which have been preheated in ozonized air, indicates that a saving in time of 40 to 50% to produce the same drying effect may be attainedby preheating the fibrous material in ozonized air:

Average saving in drying time by the use of ozonized air, as indicated by hot resistance measurements It will be seen from the above table that an average saving of time of 46.7% may be obtained by preheating the fibrous-insulated conductors in ozonized air.

The insulation varnish used was composed of an asphalt-um gum, linseed oil and benzine in the following proportions:

Per cent Asphaltum gum 30 Linseed oil 15 Benzine 55 It will be understood, however, that my process is not limited to the particular insulation varnish used, as it may be utilized with any insulation varnish containing a suitable-gum, such as asphalt, rosin ester or copal; a suitable vegetable drying oil, such as linseed or China wood oil; and a'suitable thinner, such as benzine or turpentine. In the experiments made, the insulating varnish used is known as a short oil varnish. Such varnishes contain a comparatively small percentage of oil. lVhen a long oil varnish containing a comparatively large percentage of oil is used, the preheating in ozonized air will be still more effective in reducing the drying time of the varnish film.

The treatment with ozonized air not only enables the vegetable fibrous material to become-combined or saturated with ozone, but it also has the eiiect of increasin the tensile strength of the fibrous material, as is set forth in my copending application, Serial No. 206,133, filed on July 15, 1927, and assigned to the Westinghouse Electric & Manu acturing Company.

It will also be understood that, if desired, the drying time of the varnish film may be further expedited by drying it in ozonized air after the varnish has been applied, as described in' application, Serial No. 205,504, filed by Leroy U. Spence onjAugust 27, 1927, which is also assigned to the lVestinghouse Electric & Manufacturing Company.

My invention is also applicable in hastening the drying of varnish films applied to fibrous-insulated coils wound' upon each other to a considerable depth, such as those used in transformers. The drying of an insulating varnish applied to electrical apparatus of this type, under ordinary conditions, is very slow. It has been found, however, that, when the fibrous-insulated coils are preheated in ozonized air and an insulating varnish is subsequently applied and baked, the drying of the varnish film is much accelerated. L

The temperature at which the fibrousin sulated conductors or coils are preheated in ozonized air may vary from any temperature above room temperature and the te1nperature at which the fibrous insulation begins to decompose. I prefer to use a temperature between 100 and 110 C. At temperatures below C., the ozone does not have much effect upon the fibrousinsulation, and, at temperatures above 135 C. it has the tendency to decompose the insulation. The ozone concentration may vary between 0.1 and 2 per cent and the time of preheating required may vary between one-half and thirty-two hours, depending upon the ozoneiconcentration and the temperature.

The term elevated temperature, as usedin the claims, means any temperature above room temperature and below the temperature at which the fibrous material begins to decompose.

Various other modifications of my invention may be made by those skilled in the art without departing from the spirit of my 1nvention. I desire, therefore, that only such limitations shall be imposed upon my invention as are required by the prior art and the appended claims.

I claim as my invention 1. In the method of treating fibrous insulation, the steps which comprisepreheating the fibrous insulation in ozonized air and then impregnating the same'with an insulating varnish.

' 2. In the method of treating fibrous-insulated conductors, the steps which comprise preheating the fibrous-insulated conductors in ozonized air and then impregnating the same with an insulating varnish.

3. The methodof treating fibrous-insulated conductors which comprises preheating the fibrous-insulated conductor in ozonized air, applying a varnish film, and then drying the varnish film, the ozone, combined with the fibrous-insulation, serving to hasten the drying of the subsequently-applied varnish film.

4. The method 0t treating fibrous-insulated conductors which comprises preheating the fibrous-insulated conductor in ozonized air,

applying an insulating-varnish film to the fibrous-insulated conductor, and then applying heat to dry the varnish film.

5. The method of treating fibrous-insulated conductors embedded in the slots of electrical apparatus which comprises preheating said electrical apparatus, with the fibrous-insulated conductors embedded in their respective slots in ozonized air and then immersing the same in insulating varnish.

6. The method of treating fibrous-insulated conductors embedded in the slots of electrical apparatus which comprises preheating said electrical apparatus, with the fibrous-insulated conductors embedded in their respective slots, in ozonized air, immersing the same in an insulating varnish, and heating to dry the varnish film.

7 The method of treating fibrous-insulated conductors which comprises preheating the fibrous-insulated conductor in ozonized air, applying a varnish film to the same, and then drying the varnish film in ozonized air at an elevated temperature.

8. The method of treating fibrous-insulated conductors which comprises preheating the fibrous-insulated conductor in ozonized air at a temperature of 70 to 135 (1., applying a varnish film to the same, and then drying the varnish film.

9. The method of treating fibrous-insulated conductors which comprises. preheating the.

one-half to 32 hours, applying a varnish filmto the same, and then drying the varnish film.

11. The method of treating fibrous-insulated conductors which comprises preheating the insulated conductor in ozonized air to strengthen the fibrousmaterial and to saturate it with ozone, and applying an insulating varnlsh containing a resin, a vegetable drying oil and a volatile thinher tothe insulated conductor, the ozonized air and ozonated fibers acting to expedite the oxidation of theoil and the drying of the insulating-varnish film.

12; The method of treating fibrous-insulated conductors which comprises preheating the ihsulated conductor in ozonized air to strengthen the fibrous material and to saturate it with ozone, applying an insulatlng varnish containing asphalt, a vegetable drying oil and'a volatile thinner, and then continuing the heating at an elevated temperature, the ozonized air and ozonated fibers acting to expedite the oxidation of the oil and the drying of the insulating varnish.

13. The method oftreating fibrous-insulated conductors which comprises preheating the same in ozonized air having a concentration ofabout 0.25 percent ozone until they have attained a temperature of about 105 C., cooling the same toabout 70 (3., impregnating the insulated conductors with an insulating varnish, and continuing the heating at an elevated temperature until the varnish is dry.

14. The method of treating fibrous-insulatedconductors which comprises preheating the same in an atmosphere of ozonized air having a concentration of about 0.25 percent ozone until they have attained a term perature of about. 105 C., cooling the same to about 70 C. in the same atmosphere, impregnating the insulated conductors with an insulating varnish and continuing the heating at an elevated temperature until the varnish is dry.

In testimony whereof, I have hereunto subscribed my name this 30th day of December,

P. B. COGHRAN. 

